Studies to establish an optimal diet for the decapod crab Carcinus maenas under culture conditions

The maintenance of a uniform diet for Carcinus maenas (L.), where this crab is used as test animal in the laboratory, precludes the use of fresh food, e. g. mussels, for many reasons; not the least of these is the seasonal variation in the nutritive value of such food. Different types of fresh food are variably accepted by C. maenas, dependent on such factors as taste and the consistency of the food. The crabs will eat freeze-dried food set in agar-agar. A diet of this food is, however, inferior to one of fresh food as its preparation destroys essential substances and storage causes aging. In order to eliminate these disadvantages, a better quality artificial diet was developed, one which nevertheless does not attain the quality of fresh food. This diet can be further improved by varying the proportions of the individual constitutents.     

关于欧盟植物保护品对鸟类和哺乳动物的风险评估的反思：过去、现在和未来

植物保护品在农作物上的使用会导致鸟类和哺乳动物接触有毒化学物质。在欧盟,关于此类暴露的风险评估均以当前(2009)欧洲食品安全局(EFSA)颁布的指导性文件为依据,与之前的版本相比,该文件在理论风险评估的可实现性方面有所提高(SANCO/4145/2000)。自从7年前实施2009 EFSA 指导性文件以来,基于此已经对众多植物保护品的毒性进行了成功地评估。然而,在今后的修订版本中仍然存在需要改进的重要方面。这篇焦点文章讨论了目前方案的风险评估经验,包括输入参数的保守水平和监管当局的解释以及如何在不远的将来对指导性文件进行修订提出建议。明确了推进指导文件的几方面建议,例如与生态相关的鸟类和哺乳动物生殖端点的推导和情境风险评估中建模方法的使用。在完善现有数据库方面,本文也有所强调,包括校对全欧洲相关焦点物种和扩大食物残留数据库。为了能够在将来形成一个真实可用的指导性文件,强烈建议在产业、监管和欧洲食品安全局等部门之间进行开放和建设性的沟通和交流。这样的合作也将鼓励会员国之间的融合,从而减轻产业和监管机构工作负荷。
精选自Amy C. Brooks, Mike Fryer, Alan Lawrence, Juan Pascual, Rachel Sharp. Reflections on bird and mammal risk assessment for plant protection products in the European Union: past, present and future. Environmental Toxicology and Chemistry: Volume 36, Issue 3, pages 565–575, July 2017. DOI: 10.1002/etc.3719
详情请见http://onlinelibrary.wiley.com/wol1/doi/10.1002/etc.3719/full
     

Accumulation of paralytic shellfish poisoning toxins in planktonic copepods during a bloom of the toxic dinoflagellate<Emphasis Type="Italic"> Alexandrium tamarense</Emphasis> in Hiroshima Bay,western Japan

Concentrations of paralytic shellfish poisoning (PSP) toxins in toxic dinoflagellate cells and in marine planktonic copepods were monitored during the bloom of Alexandrium tamarense in Hiroshima Bay, western Japan. Concentration of the toxins retained by copepods was a function of the ambient toxin concentration, i.e. the product of A. tamarense cell density and cellular toxicity. The toxin concentration in copepods increased with the increase of toxicants in the seawater then leveled off, but decreased significantly at higher concentrations. In the field, the maximum toxin concentration was 1.2 pmol ind^-1, whereas in the laboratory, the copepod Acartia omorii accumulated a much higher concentration of PSP toxins (24 pmol ind^-1). Feeding avoidance against Alexandrium tamarense and a shift to alternative food sources such as diatoms in the field might keep their toxin levels lower than their potentially maximum level. The copepod toxin levels in the field were not so high as to cause an instantaneous lethal effect on their predator fishes but may reach possibly lethal levels after a few days' continuous feeding. Overall toxin retention by copepods after 12 h feeding and 2 h starvation was only 2.5% of total ingested toxins, which suggested that a significant amount of toxins was released into the seawater. Measurements of toxin reduction and gut evacuation suggested that the toxins were removed through both fecal evacuation and metabolism (e.g. excretion, decomposition and transformation). The results, as a whole, imply that copepods can be a link for PSP toxin flux in both pelagic and benthic food webs and can also be a sink for toxins by metabolizing and removing them from the environment.Communicated by T. Ikeda, Hakodate     

Uptake,transformation, and elimination kinetics of paralytic shellfish toxins in white seabream (<Emphasis Type="Italic">Diplodus sargus</Emphasis>)

Marine toxins generated by harmful algal blooms can be transferred through the marine food web and ultimately cause massive deaths of piscivorous predators. However, very few studies have explored the processes of accumulation and biotransformation of paralytic shellfish toxins (PSTs) within fishes. White seabream (Diplodus sargus) were orally challenged with contaminated cockles (Cerastoderma edule) containing N-sulfocarbamoyl and decarbamoyl toxins and non-contaminated cockles afterwards. Specific PSTs that occurred in low abundance in cockles (B1 7.6% and dcSTX 1.6% molar fraction) were the only toxins detected in fish viscera possibly resulting from selective elimination and transformation of the various PSTs. Concentration of toxins progressively increased in fish viscera throughout the uptake period. Toxins were then rapidly depurated (B1 0.905 day⁻¹, dcSTX 0.467 day⁻¹) when diet was changed to non-toxic cockles. Results indicate conversion of a precursor toxin into B1 which in turn might be converted into dcSTX at a lower extent. Low accumulation efficiency of 1.7 and 5.0% was calculated to B1 and dcSTX, respectively. This study contributes to a better understanding of dynamics of PSTs in fish and the fate of these compounds in the marine food web.     

Environmental and genetic influences on mating strategies along a replicated food availability gradient in guppies (Poecilia reticulata)

Food availability is expected to influence the relative cost of different mating tactics, but little attention has been paid to this potential source of adaptive geographic variation in behavior. Associations between the frequency of different mating tactics and resource availability could arise because tactic use responds directly to food intake (phenotypic plasticity), because populations exposed to different average levels of food availability have diverged genetically in tactic use, or both. Different populations of guppies (Poecilia reticulata) in Trinidad experience different average levels of food availability. We combined field observations with laboratory “common garden” and diet experiments to examine how this environmental gradient has influenced the evolution of male mating tactics. Three independent components of variation in male behavior were found in the field: courtship versus foraging, dominance interactions, and interference competition versus searching for mates. Compared with low-food-availability sites, males at high-food-availability sites devoted more effort to interference competition. This difference disappeared in the common garden experiment, which suggests that it was caused by phenotypic plasticity and not genetic divergence. In the diet experiment, interference competition was more frequent and intense among males raised on the greater of two food levels, but this was only true for fish descended from sites with low food availability. Thus, the association between interference competition and food availability in the field can be attributed to a genetically variable norm of reaction. Genetically variable norms of reaction with respect to food intake were found for the other two behavioral components as well and are discussed in relation to the patterns observed in the field. Our results indicate that food availability gradients are an important, albeit complex, source of geographic variation in male mating strategies.     

Encapsulation of bioactive compounds using nanoemulsions

Roughly one-third of the food produced in the world for human consumption every year, approximately 1.3 billion tonnes, gets lost or wasted, according to the Food and Agriculture Organization (FAO). There is therefore an urgent need for new methods to preserve food. Encapsulation using nanoemulsions is a powerful technique for the protection of food-grade ingredients including vitamins, lipids, antioxidants and antimicrobial agents. In general, nanoemulsion systems demonstrate superior characteristics over conventional emulsions. This is due to their smaller droplet size, transparent optical properties, higher physical stability against droplet destabilization factors and improved bioavailability of the entrapped active ingredients. In general, nanoemulsions have been prepared with different sizes of droplets. However, a droplet size higher than 200 nm is generally preferred for food applications. Here we review nanoemulsion compositions, types of active ingredients, applications in different types of food systems, toxicological and safety aspects, and future directions.     

Balkan endemic nephropathy and aristolochic acid I: an investigation into the role of soil and soil organic matter contamination,as a potential natural exposure pathway

Aristolochic acids (AAs) are carcinogenic and nephrotoxic plant alkaloids present in Aristolochia species, used in traditional medicine. Recent biomolecular and environmental studies have incriminated these toxins as an etiological agent in Balkan endemic nephropathy (BEN), a severe kidney disease occurring in the Balkan Peninsula. The questions on how the susceptible populations are exposed to these toxins have not yet been clearly answered. Exposure to AAs through the food chain, and environmental pollution (soil/dust), could provide an explanation for the presence of BEN in the countries where no folkloric use of the plant has been documented (Bulgaria, Croatia). Additional exposure pathways are likely to occur, and we have shown previously that AAs can contaminate crop plants through absorption from soil, under controlled laboratory environment. Here, we attempt to provide additional support to this potential exposure pathway, by revealing the presence of AAI in soil and soil organic matter samples collected from BEN and non-BEN areas. The samples were processed in order to be analyzed by high-pressure liquid chromatography, and ion trap mass spectrometry. Our results showed the presence of AAI in small concentrations, both in BEN and non-BEN soils, especially where Aristolochia plants and seeds were present.     

Amphibian myiasis. Blowfly larvae (Lucilia bufonivora,Diptera: Calliphoridae) coping with the poisonous skin secretion of the common toad (Bufo bufo)

The blowfly Lucilia bufonivora shows high host specificity for toads despite the host’s toxic skin secretion, which consists mainly of bufadienolides. These toxins are effective blockers of the Na⁺, K⁺-ATPase, an enzyme that is essential for many physiological processes in animals. Whereas common toad (Bufo bufo) toxins were identified in the larvae of the fly, few toxins were found in the pupae and empty puparia as trace amounts, while adult flies were entirely free of these toxic compounds. Similar results were obtained when larvae of generalist necrophagous blowflies (L. sericata, Calliphora vicina) fed on toad carcasses. Analysis of the Na⁺, K⁺-ATPase gene revealed no amino acid substitution at positions known to mediate resistance to bufadienolides in other systems. Alternative mechanisms of resistance such as efficient excretion of the compounds may enable the flies to use this poisonous food source.     

Nanotechnology applications in pollution sensing and degradation in agriculture: a review

With the rise in the global population, the demand for increased supply of food has motivated scientists and engineers to design new methods to boost agricultural production. With limited availability of land and water resources, growth in agriculture can be achieved only by increasing productivity through good agronomy and supporting it with an effective use of modern technology. Advanced agronomical methods lay stress not only on boosting agricultural produce through use of more effective fertilizers and pesticides, but also on the hygienic storage of agricultural produce. The detrimental effects of modern agricultural methods on the ecosystem have raised serious concerns amongst environmentalists. The widespread use of persistent pesticides globally over the last six decades has contaminated groundwater and soil, resulting in diseases and hardships in non-target species such as humans and animals. The first step in the removal of disease causing microbes from food products or harmful contaminants from soil and groundwater is the effective detection of these damaging elements. Nanotechnology offers a lot of promise in the area of pollution sensing and prevention, by exploiting novel properties of nanomaterials. Nanotechnology can augment agricultural production and boost food processing industry through applications of these unique properties. Nanosensors are capable of detecting microbes, humidity and toxic pollutants at very minute levels. Organic pesticides and industrial pollutants can be degraded into harmless and often useful components, through a process called photocatalysis using metal oxide semiconductor nanostructures. Nanotechnology is gradually moving out from the experimental into the practical regime and is making its presence felt in agriculture and the food processing industry. Here we review the contributions of nanotechnology to the sensing and degradation of pollutants for improved agricultural production with sustainable environmental protection.     

Die Bedeutung von Lebensmitteln tierischer Herkunft für die Mykotoxinaufnahme beim Menschen

Mycotoxins are a heterogeneous group of secondary fungal metabolites. Their formation in food and feedstuffs is influenced by many factors, including humidity, temperature, pH, oxygen concentration, type of substrate or presence of competitive microflora. The Food and Agriculture Organisation of the United Nations estimated in 1985 that approximately 25% of the world’s grain supply is contaminated with mycotoxins. There are more than 300 known mycotoxins; however, due to their occurrence and concentrations in food, and their toxic potential, only few of these are relevant with regard to consumer protection. These include the aflatoxins, ochratoxins and trichothecenes like deoxynivalenol, zearalenone and fumonisins. In Germany, only aflatoxins in food and feedstuffs are subjected to legal regulations. Beside the negative effects of mycotoxins on health and performance of farm animals, it is of importance to consider to what extent mycotoxins might be carried over into edible tissues like meat, milk and eggs when fed to farm animals. The present review shows that the carry over of mycotoxins into edible tissues is relatively low and is dependent on the specific mycotoxin and animal species. For example, due to the microbial decomposition of mycotoxins in the rumen, the carry over of mycotoxins into edible tissues of ruminants is considerably lower compared to monogastric species (pigs, chickens). Furthermore, after a short withdrawal period of 4 to 14 days combined with the feeding of non-contaminated diets, most of the mycotoxins, aside from ochratoxin A, are no longer detectable in any edible tissue. Ochratoxin A has a high binding affinity to specific blood proteins and is reabsorbed in the kidney; these mechanisms delay its elimination and increase the withdrawal period to at least 4 weeks. However, aside from the concentration of these substances in food, the daily intake of contaminated food is important for the risk analysis of mycotoxins to humans. In a recent study, it has been shown that more than 50% of the daily intake of ochratoxin A is derived from cereals and cereal products, and 30% from red wine, coffee and beer. Mear products from pigs and chickens only account for 4% of the total intake, while products from ruminants are considered to be negligible. These results indicate that mycotoxin-contaminated edible tissue, as compared to plant products, only plays a minor role with respect to consumer protection.     

Experimental increase in food supply influences the outcome of within-family conflicts in Tengmalm’s owl

Within a family there are conflicts of interest between parents and offspring, and between male and female parents, over the supply of parental care. The observed pattern of parental care is the outcome of negotiations within the family, and may be influenced by environmental factors such as food abundance. We experimentally increased food supply to ten Tengmalm’s owl (Aegolius funereus) nests from hatching to fledging, mimicking natural cached prey. Ten un-supplemented nests served as controls. Parents and offspring were fitted with radio-tags. Food provisioning by parents was measured both in the (1) mid- and (2) late nestling stage and in the (3) early and (4) late post-fledging stage. In response to food supplementation, both males and females reduced food provisioning, but the effect was more pronounced in females. Females generally contributed much less to food provisioning than males, and food supplementation increased the difference between the sexes. Mass loss during the brooding stage was substantially lower for supplemented than for control females. Food supplementation did not improve offspring survival, and had no effect on body measurements of nestlings. In conclusion, parents of both sexes used the increased food supply to reduce the costs of caring for their current offspring, but females responded more strongly than males.     

Toxicity of Brachuryan crabs in India

Crabs are the most abundant macrofauna in the coastal environment, and may belong to many different species and even families. Some of these crabs contain specialized protein substances that act as toxins. Toxins, especially proteins that are produced by living cells or organisms, are poisonous substances. Toxins can be divided according to their pharmacological effects (neurotoxins, myotoxins, hepatotoxins, nephrotoxins, hematological toxins, and locally acting toxins) and their sources, such as snakes, scorpions, mussels, spiders, marine creatures, or sea anemones. Crab toxins are heat resistant and are found in the crabs’ viscera. Hence, they cannot be destroyed by cooking, and there is also no known treatment available for these toxins. The only alternative is to educate fishermen, holiday makers, and seafood consumers to recognize these poisonous species and avoid them. Several toxins identified from crabs are neurotoxins, related to tetradotoxin (TTX), which is found in pufferfish. Other toxins include saxitoxin (STX), neurosaxitoxin (NeoSTX), and some unidentified toxins. Some poisonous crabs possess a mixture of these toxins. This article describes the toxins and Brachuryan crabs producing toxicity.     

Limits of Concern: suggestions for the operationalisation of a concept to determine the relevance of adverse effects in the ERA of GMOs

Background

The European Food Safety Authority proposed a concept for the environmental risk assessment of genetically modified plants in the EU that is based on the definition of thresholds for the acceptability of potential adverse effects on the environment. This concept, called Limits of Concern (LoC), needs to be further refined to be implemented in the environmental risk assessment of genetically modified organisms.

Methods

We analyse and discuss how LoC can be defined for the environmental risk assessment for three different types of genetically modified plants. We outline protection goals relevant to the genetically modified plants in question and discuss existing concepts and suggestions for acceptability thresholds from the environmental risk assessment of different regulatory areas. We make specific recommendations for the setting and use of LoC for each type of genetically modified plant.

Results

The LoC concept can be suitably applied for the environmental risk assessment of genetically modified organisms, if the different protection goals in agro-environments are specifically considered. Not only biodiversity protection goals but also agricultural protection goals need to be addressed. The different ecosystem services provided by weeds inside and outside agricultural fields have to be considered for genetically modified herbicide-tolerant crops. Exposure-based LoCs are suggested based on knowledge about dose–effect relationships between maize pollen and non-target Lepidoptera for insect-resistant maize. Due to the long-term nature of biological processes such as spread and establishment, LoCs for genetically modified oilseed rape should be defined for the presence of the genetically modified plant or its genetically modified traits in relevant protection goals.

Conclusions

When setting LoCs, the focus should be on protection goals which are possibly affected. Potential overlaps of the LoC concept with the ecosystem service concept have to be clarified to harmonise protection levels in the agro-environment for different stressors. If additional impacts on agro-biodiversity resulting from the cultivation of genetically modified plants are to be avoided, then high protection levels and low thresholds for acceptable effects (i.e. LoC) should be set.

     

Food availability,intrusion pressure and territory size: an experimental study of Anna's hummingbirds (Calypte anna)

Theoretical considerations implicate food availability and intrusion pressure as important determinants of territory size, but empirical studies have led to contradictory conclusions about cause-and-effect relationships among these three variables. To investigate this problem, we provided patches of electronically controlled artificial flowers, which were defended by male Calypte anna. Food availability was experimentally manipulated, and intrusion rate and territory size were calculated from behavioral observations of the territory owner. Changes in both food availability and intrusion rate were found to be significantly correlated with changes in territory size under certain conditions. Intrusion rate, which was influenced by food availability, was negatively associated with territory size so long as food availability was high. This association persisted even after possible effects of food availability were controlled statistically. Food availability was negatively correlated with territory size only when intrusion rates were high and after owners had been defending territories for 3 days. As food availability and intrusion rate increased, owners increasingly restricted their defense to the patch itself; partial regressions revealed a significant association for intrusion rate but not food availability. When intrusion rate was low and food availability varied from low to high levels, no relationship was observed between food availability and territory size, apparently because of opposing influences of food abundance on territory size. Correspondence to: P.W. Ewald     

Assessing the capacity of three Bolivian food systems to provide farm-based agroecosystem services

ABSTRACT

Food system activities have modified 40% of the Earth’s terrestrial surface. These activities affect the sustainability of food systems – and their ability to provide agroecosystem services. Here, we compare three food systems in Bolivia. One is agro-industrial (soybean), one is indigenous to a Guarani community (maize and beans), and one is an agroecological, horticulture-based food system. We use the Agroecosystem Service Capacity (ASC) approach, which is based on a list of 23 agroecosystem services that allow the ASC index of farm-based agroecosystems to be estimated. Our findings show that agroecological (ASC = 2.57) and indigenous (ASC = 2.43) farm-based agroecosystems have a higher capacity to provide farm-based agroecosystem services than the agro-industrial (ASC = 0.82). This capacity differs because farmers in the agroecological and indigenous farm-based agroecosystems achieve a higher structural diversity and know how to use more agroecosystem services. These results could promote more sustainable food systems by fostering agricultural landscapes that provide a diversity of farm-based agroecosystem services.     

Sequestration of plant secondary compounds by butterflies and moths

Summary A number of aposematic butterfly and moth species sequester toxic substances from their host plants. Some of these insects can detect the toxic compounds during food assessment. Some pipevine swallowtails use aristolochic acids among the host finding cues during oviposition and larval feeding and accumulate the toxins in the body tissues throughout all life stages. Likewise, a danaine butterfly,Idea leuconoe, which sequesters high concentrations of pyrrolizidine alkaloids in the body, lays eggs in response to the specific alkaloid components contained in the apocynad host. Insect species sharing the same poisonous host plants may differ in the degree of sequestration of toxins. Two closely ralated aposematic geometrid moth species,Arichanna gaschkevitchii andA. melanaria, sequester a series of highly toxic diterpenoids (grayanotoxins) in different degrees, while a cryptic geometrid species,Biston robstus, does not sequester the toxins, illustrating the diversity in adaptation mechanisms even within the same subfamily. By contrast, a number of lepidopteran species store the same compounds though feeding upon taxonomically diverse plant species. A bitter cyanoglycoside, sarmentosin, was characterised from several moth species in the Geometridae, Zygaenidae and Yponomeutidae, and from the apollo butterflies,Parnassius spp. (Papilionidae), although each species feeds on different groups of plants.Interspecific similarities and differences in life history and ecology are discussed in relation to variable characteristics of sequestration of plant compounds among these lepidopteran insects.     

How do slugs cope with toxic alkaloids?

Summary. Arion lusitanicus and other slugs are able to feed on a variety of plants, even those containing toxic secondary metabolites, such as alkaloids. Alkaloids, like sparteine, lupanine, quinidine and atropine are avoided in no-choice feeding experiments only when they are present in concentrations above 1 mg/g food pellet. Alkaloids (sparteine, lupanine, cytisine, quinidine, atropine, senecionine, eserine, and harmaline) are toxic to Arion lusitanicus when injected. LD₅₀ values are 10 to 20 fold higher than in vertebrates indicating that slugs have a high tolerance towards food toxins. The tolerance is higher in young animals than in adult slugs. Injected alkaloids are rapidly detoxified within 72 h. Tolerance and detoxification can be induced by feeding slugs on non-lethal doses of lupin alkaloids. Using isolated microsomal preparations from the digestive gland, active detoxification was observed in vitro. Evidence is presented that cytochrome p450 plays an important role in detoxification of the applied alkaloids. A powerful and inducible detoxification systems appears to be the main mechanism that allows slugs to feed on plants rich in secondary metabolites (when no other food is available), that are usually avoided by other herbivores.     

Edible films and coatings for food packaging applications: a review

Environmental Chemistry Letters - Food preservation technologies are currently facing challenges in prolonging the shelf life of perishable food products. The uses of edible films and coatings...     

Food and predators affect egg production in song sparrows

Although the possibility that food and predators may interact in limiting avian populations has long been recognized, there have been few attempts to test this experimentally in the field. We conducted a manipulative food addition experiment on the demography of Song Sparrows (Melospiza melodia) across sites that varied in predator abundance, near Victoria, British Columbia, Canada, over three consecutive breeding seasons. We previously showed that food and predators had interactive effects on annual reproductive success (young fledged per female). Here, we report the effects on egg production. Our results show that food limits the total number of eggs laid over the breeding season ("total egg production") and that interactive food and predator effects, including food effects on nest predation, determine how those eggs are "parceled out" into different nests. Food addition alone significantly affected total egg production, and there was no significant interannual variability in this result. At the same time, both food and predators affected the two determinants of total egg production: "clutch number" (total number of clutches laid) and average clutch size. Both clutch number and size were affected by a food x predator x year interaction. Clutch number was lower at low-predator locations because there was less nest predation and thus less renesting. Food addition also significantly reduced nest predation, but there was significant interannual variation in this effect. This interannual variation was responsible for the food x predator x year interactions because the larger the effect of food on nest predation in a given year, the smaller was the effect of food on clutch number; and the smaller the effect of food on clutch number, the larger was the effect of food on clutch size. Potential predator and year effects on total egg production were thus cancelled out by an inverse relationship between clutch number and clutch size. We suggest that combined food and predator effects on demography could be the norm in both birds and mammals.     

The effects of aggregation on the performance of the inverse method and indicators of network analysis

Food webs are usually aggregated into a manageable size for their interpretation and analysis. The aggregation of food web components in trophic or other guilds is often at the choice of the modeler as there is little guidance in the literature as to what biases might be introduced by aggregation decisions. We examined the impacts of the choice of the a priori model on the subsequent estimation of missing flows using the inverse method and on the indices derived from ecological network analysis of both inverse method-derived flows and on the actual values of flows, using the fully determined Sylt-Rømø Bight food web model. We used the inverse method, with the least squares minimization goal function, to estimate ‘missing’ values in the food web flows on 14 aggregation schemes varying in number of compartments and in methods of aggregation. The resultant flows were compared to known values; the performance of the inverse method improved with increasing number of compartments and with aggregation based on both habitat and feeding habits rather than diet similarity. Comparison of network analysis indices of inverse method-derived flows with that of actual flows and the original value for the unaggregated food web showed that the use of both the inverse method and the aggregation scheme affected indices derived from ecological network analysis. The inverse method tended to underestimate the size and complexity of food webs, while an aggregation scheme explained as much variability in some network indices as the difference between inverse-derived and actual flows. However, topological network indices tended to be most robust to both the method of determining flows and to the inverse method. These results suggest that a goal function other than minimization of flows should be used when applying the inverse method to food web models. Comparison of food web models should be done with extreme care when different methodologies are used to estimate unknown flows and to aggregate system components. However, we propose that indices such as relative ascendency and relative redundancy are most valuable for comparing ecosystem models constructed using different methodologies for determining missing flows or for aggregating system components.